The active April sky

There is plenty to see in April, which brings us the first warm observing nights of the year. The trademark Lyrid shower will be a wash thanks to a nearly full moon drowning out most of the meteors during the nights the shower peaks.

Tomorrow night, the waning crescent moon will be 6 degrees (about three finger-widths) northwest of Mercury in the east before dawn.

Check this out: Mercury through a telescope is also a crescent. Since Mercury is inferior (closer to the sun), we can never observe a "full" Mercury. Like Venus, the other inferior world, Mercury advances through a phasic cycle. When Galileo observed Venus through his own telescope and saw that it was in a crescent phase similar to the moon's, it solidifed his notion that the sun, not Earth, was at the center of the solar system.

On Friday, April 12, Pluto will be stationary, meaning that its apparent westward motion seems to freeze and it appears to reverse course toward the east. This reverse trek, called retrograde, is an illusion resulting from our own perspective.

As we watch Pluto from a faster moving planet, it seems to turn around when we outlap it. Eventually, it will seem to stop again before resuming prograde motion. Pluto is invisible without a powerful telescope, but if an observer tracked its motion over several weeks, he or she can expect Pluto to begin a new retrograde loop tonight.

We end the month with Saturn, the most ornate planet, adopting the sky's starring role. By Sunday, April 28, Saturn is rising at sunset and will be visible all night.

SKY CALENDAR

April 10 - New moon. This is the best time of the month to observe faint objects like galaxies and star clusters because there is no moonlight to interfere. Find a location with little to no light pollution and enjoy the nearly perfect observing conditions. You'll probably even be able to make out the Milky Way!

April 14 - Conjunction of the moon and Jupiter. The Moon will pass about two degrees of the giant planet Jupiter in the evening sky. The crescent moon will be at magnitude -10.6 and Jupiter will be at magnitude -2.1. Look for both objects in the west after sunset. The pair will be visible in the evening sky for about three hours after sunset.

April 21, 22 - Lyrids meteor shower. The Lyrids is an average shower that usually produces about 20 meteors per hour at its peak. It is produced by dust particles left behind by comet C/1861 G1 Thatcher, which was discovered in 1861. The shower runs annually from April 16 to 25. It peaks this year on the night of the night of the 21st and morning of the 22nd. These meteors can sometimes produce bright dust trails that last for several seconds. The nearly full moon will be a problem this year, blocking out all but the brightest meteors. Meteors will radiate from the constellation Lyra, but can appear anywhere in the sky.

April 25 - Full moon. This full moon was known by early Native-American tribes as the Full Pink Moon because it marked the appearance of the moss pink, or wild ground phlox, one of the first spring flowers. This year, it is also known as the Paschal Full Moon because it is the first full moon of the spring season.

April 28 - Saturn at opposition. The ringed planet will be at its closest approach to Earth and its face will be fully illuminated by the sun. This is the best time to view and photograph Saturn and its moons. A medium-sized or larger telescope will allow you to see Saturn's rings and a few of its brightest moons.

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